Newbie question on reading pixel color

[efo]

Hi guys,

I am a newbie and I am trying to figure out a a simple program using a c interface and imagemagick. First I have to load a picture and reduce the number of colors to a given number (e.g. 8). Next, I have to read the pixel colors one by one.
I got across and example to read pixel color and I stripped it down to:

MagickWandGenesis();
wand=NewMagickWand();
MagickReadImage(wand,argv[1]);
PixelWand **pixels;
iterator=NewPixelIterator(wand);
unsigned long width;
MagickPixelPacket pixel;

wpxl=MagickGetImageWidth(wand);
hpxl=MagickGetImageHeight(wand);

for (y=0; y < hpxl; y++)
{
pixels=PixelGetNextIteratorRow(iterator,&width);
for (x=0; x < wpxl; x++)
{
PixelGetMagickColor(pixels[x],&pixel);
printf("%d %d => %f %f %f \n",x,y,pixel.red,pixel.green,pixel.blue);
}
}

Something I dont fully understand is why pixels is ** and not * if only one row at a time is read into it. Aslo, do I really need an iterator? Isnt there a function that allows me to access pixels directly (e.g. color= function(wand,x,y) or pixels=function(wand,x1,y1,x2,y2) and PixelGetMagickVolor(pixels[x,y],&pixel))?

Sorry for the dumb questions but I am having hard time finding detailed documentation on the matter.

Thanks.

Efo

[magick]

MagickWand applies object-oriented principles to a procedural language, C. If you would like direct access to the image pixels, use MagickCore. In MagickCore, use this code snippet to access pixel values:

Code: Select all

  for (y=0; y < (long) image->rows; y++)
  {
    p=AcquireImagePixels(image,0,y,image->columns,1,&image->exception);
    if (p == (const Image *) NULL)
      break;
    for (x=0; x < (long) image->columns; x++)
    {
      (void) printf("%d %d: %d %d %d\n",y,x,p->red,p->green,p->blue);
      p++
    }

[efo]

Thank you Magick,

That's what I was looking for!!! (or better AcquireOneMagickPixel).
Can you suggest any good readings for MagickCore?

Thanks again!

Efo

[magick]

We aspire to write a book about MagickWand and MagickCore but so far we can't find the time. In the mean-time all we have is the ImageMagick source code which is written in MagickCore and the API details at http://www.imagemagick.org/script/magick-core.php.